Which antidote is used for cyanide toxicity?

Sodium thiosulfate is the antidote used for cyanide toxicity because it acts as a sulfur donor that helps in the detoxification of cyanide into thiocyanate, a much less toxic compound. In the body, sodium thiosulfate combines with cyanide to form thiocyanate, which can be safely excreted by the kidneys. This process mitigates the harmful effects of cyanide, which binds to cytochrome c oxidase in the mitochondria, inhibiting cellular respiration and leading to hypoxia.

Other substances listed do not address cyanide toxicity specifically. Calcium gluconate is used primarily for treating hypocalcemia or magnesium overdose; activated charcoal is useful for various types of poisoning by absorbing toxins in the gastrointestinal tract but is not effective for cyanide once it has been absorbed into the bloodstream; and Vitamin K is essential for blood clotting and is used in cases of anticoagulant overdose, but it has no role in treating cyanide poisoning. Thus, sodium thiosulfate is the specific antidote for cyanide exposure due to its unique ability to convert cyanide into a safer compound for the body.